The present invention relates to an electrically controlled printing unit, adapted particularly, but not exclusively, to be used in a typewriter.
A printing unit is known comprising a control circuit of electronic type, a fixed support guide and a printing assembly movable along the guide. The printing assembly generally comprises a type or character bearing element, a printing ribbon preferably contained in a corresponding cartridge, and a plurality of mechanical or electromechanical actuators controlled by the control circuit and adapted to allow the printing assembly to perform a plurality of functions. The functions may be, for example, the selection of a character, return of the printing assembly by one step, programming, normally indicated by the term "tabulation" of movements of the printing assembly by several steps forward or backward along the guide, etc. while service functions may be, for example, the striking of a character, advance of the printing assembly by one step after each striking action, feed of the printing ribbon, raising of the corresponding cartridge, etc.
In the above described known printing unit, the number of the actuators is generally proportional to the number of functions that the printing assembly is capable of performing, since each of the functions requires, for its own performance, the use of at least one actuator, which may be constituted by an electromagnet, a directcurrent motor or a stepping motor. Each of the actuators is controlled by a corresponding control assembly forming part of the control circuit and which, in the event of the actuator being a directcurrent motor, is an analogue control assembly.
The relatively high number of actuating means and of the corresponding control assemblies employed in the known printing unit generally entails some difficulties of carrying into effect and assembly, considerable over-all dimensions and weights and, above all, a relatively high cost of production.
The object of the present invention is to provide a printing unit capable of performing functions like those of the abovedescribed known printing unit, but which is without the economic and structural disadvantages presented by the latter and hereinbefore mentioned.